This invention relates to techniques and apparatus for wireless communication using Direct Sequence Spread Spectrum (DSSS) techniques.
In the transmitter of a direct-sequence spread spectrum communication systems, a carrier waveform is modulated by a data sequence x(n) and by a spreading sequence or code sequence C(n). The code sequence may be a pseudo-noise (PN) sequence, such as a maximum length sequence (m-sequence). The PN sequence is used to reduce the sensitivity of the communication channel to noise, reduce the power spectral density of the signal and to allow multiple communication channels to operate simultaneously. In the latter case, each channel is assigned its own PN code sequence, so the technique is called code-division multiple access (CDMA).
In the receiver the data signal is recovered by removing the carrier wave and then correlating the received signal with the PN code sequence used for transmission. Decorrelation requires a large amount of computation to align the received signal with the PN code sequence, and so adds to the cost of the receiver.
In view of the preceding remarks, it is clear that there is an unmet need in the art for a receiver that avoids the high cost of performing a correlation between the received signal and a PN code sequence.